The options are
- global which allow access to all. all current an all future
- OBS which typically allow access to all associated with an OBS unit (unit only, unit and descendant or unit and ancestors or even unit, descendants and ancestors = any unit in the specific OBS), though you might not have OBS based on the PM's. Again all current an all future
- instance which allow access to the currently named projects, all future projects would have to be added to the rights
You can give any of those to groups which is recommended if there are more than one person with the same rights. Otherwise not.
Have you established that assigning the Project Managers to be the PM's of the projects they should have access does not accomplish what you want. Or are there more than one person who should have those rights to any single project?